Study: Lunar, solar tides affect quake activity

The sun and moon are the latest targets of University of California, Berkeley earthquake research.

Their gravity has been tugging away at the San Andreas Fault the new research has quake investigators looking up instead of down.

In UC Berkeley's McCone Hall, they maintain a laboratory filled with sensitive instruments that always seem to surprise the people watching them.

"There was a magnitude 3.8 yesterday," Robert Nadau said.

Nadau is talking about earthquakes. They happen all the time -- 619 in Northern California the past week alone.

"The Holy Grail is to be able to tell when a big earthquake is coming," Nadau said.

Now, he and his team may be a little closer. They are about to publish research showing that gravity from the sun and the moon create, not quakes, but tremors.

To appreciate the significance of this discovery, it may help to explain the difference between quakes and tremors. Tremors take place at a deeper level. They may last days. They are not short and sharp, like a quake, they are more like a drag. But they indicate the kinds of stress that could lead to earthquakes.

"Well, people knew about these tremors, now we know why they are happening," Nadau said.

Twenty miles below the San Andreas Fault, Nadau's team has found a region of moist, putty-like rock. When gravity from the sun or moon pulls the fault laterally, the compressed water in that rock allows the section to slide, creating the tremors and straining the crust above.

"The thing about the tremors is they give us a picture of what is happening below where the earthquake appears," Nadau said.

And these tremors happen as predictably as the tides, bringing us one step closer to seismology's Holy Grail -- being able to predict earthquakes.